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Homework Help: Motion in a plane

  1. May 5, 2008 #1
    Have no idea how to start this probelm if anybody could help thank you

    1. The problem statement, all variables and given/known data
    A cargo ship carrying 50 tons of coffee is initially traveling North with a speed of 40 m/s. Five minutes later, the cargo ship is traveling at 20 m/s into san Fransico bay in a direction 48 degress North of East. Use a coordinate system with + x corresponding to East and +y corresponding to North to answer the following question

    a) What are the x and y components of the initial velocity?

    B) what are the x and y componenets of the final velocity?

    C) What is the change in velocity (magnitude and direction) of the ship?

    D) explain the difference b/w velocity and speed?

    2. Relevant equations

    a) No clue
    B) cos0=a/h
    sin0= o/h
    C) delta (r)/delta(t) and to get delta r i use c^2= B^2 + C^2

    3. The attempt at a solution

    a) x=0 y= 40 m/s

    If i have the equations right i don't know what to use for o and a
  2. jcsd
  3. May 5, 2008 #2


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    Science Advisor

    In other words separate the volocity into "east" and "north" components.

    Yes, of course! why did you say "no clue"?

    Draw a picture. You are told the velocity is "20 m/s into san Fransico bay in a direction 48 degress North of East." so draw a line 20 units long at 48 degrees above the x-axis (East). Draw a line from the end of that perpendicular to the x-axis so you have a right triangle with angle 48 degrees and hypotenuse 20 units long. The "near" side is the x (East) component and the y (North) component is the "opposite" side of the right triangle. Now use the trig functions you cited above to find those lengths.

    The speed changed from "40 m/s" to "20 m/s". How much change is that? The angle changed from "North" to "48 degrees North of East". How much change is that? You picture might help.

    For (D) you probably can look up the definitions of "velocity" and "speed" in your textbook.

  4. May 5, 2008 #3
    so does it look like this ? Thanx for the help
    __ _ /_|
    __ /___|_40 m/s *=48 degress
    _ / *___|

    x component is 20m/s*cos(48)=13.38
    y component is 20 m/s*sin(48)=14.86

    P.s couldn't get it to look like a triangle /_|
    Last edited: May 5, 2008
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